Wavelength tunable solid state lasers have gained considerable commercial importance because they avoid the inconvenience inherent in tunable dye lasers. U.S. Pat. No. 4,811,349 to Payne et al. discloses a new family of tunable, chromium-doped fluoride crystal laser gain media of the composition Cr.sup.+3 :XYZF.sub.6 wherein X is an alkali metal ion; Y is an alkaline earth metal ion, Cd.sup.+2 or Mg.sup.+2 ; and Z is Al.sup.+3, Ga.sup.+3 or Sc.sup.+3. These include Cr.sup.+3 :LiCaAlF.sub.6 ("Cr:LiCAF"), Cr.sup.+3 :LiSrAlF.sub.6 ("Cr:LiSAF"), and Cr.sup.+3 :LiSrGaF.sub.6 ("Cr:LiSGaF"). Unfortunately, these crystals are somewhat frangible, and tend to fracture on unequal heating, as may occur on pumping--especially longitudinal pumping with a single wavelength pump source--of uniformly doped laser hosts made therefrom where the outer surfaces are cooled except for the end faces. Because of the exponential decay of the transmission function, the intensity I of a beam transversing a crystal is EQU I=I.sub.o e(-.alpha.l)
where I.sub.0 is the initial input, .alpha. is the absorption coefficient at a given pump wavelength and l is the distance along the crystal. Absorbed energy translates into heat. Thus, much more energy (heat) is deposited at the entrance end of the host than further into the crystal. In tests with 6.35 and 5 mm diameter LiSAF rods of approximately 6 cm length, the input end of the rods shattered at 15-18 Watts input levels when almost all of the pump energy was absorbed. Stress/strain calculations and thermal deposition profiles indicated large areas of stress/strain due to high thermal gradients due to exterior surface cooling except for the endfaces, and poor thermo-mechanical material properties. This can lead to catastrophic failure of the crystal without prior warning as the input power is increased. Longitudinal pumping of a uniformly doped host can also cause localized thermal augmentation due to Excited State Absorption (ESA) and upconversion under process conditions, both of which are exacerbated by uneven pump energy absorption in accordance with the above-stated absorption formula. Further, the fluorescence lifetime in these crystals is strongly temperature dependent near room temperature, resulting in reduced stored energy in higher temperature areas and lower quantum efficiency, producing more localized heat.